1. Field of the Invention.
This invention relates to target tracking devices for use in guided vehicles. More particularly, this invention relates to tracking devices for small guided missiles, torpedoes, and the like in which it is desirable to have the nose free for carrying paraphernalia other than the tracker, and in which it is sometimes desirable to find and lock on a target behind the carrying vehicle.
2. Description of the Prior Art.
The use of trackers in guided missiles and the like is well known. A typical prior art tracker is mounted in the nose of the carrying vehicle and comprises a lens system, a sensing unit and suitable electronics. An image of the target, which may be an actual optical image, a heat image or some other type of image depending upon the type of lens system and sensing unit, impinges on the sensing unit through the lens system. The sensing unit converts information received from the target image into signals which travel through the electronics and drive various servomechanisms which keep the tracker locked on the target and navigate the carrying vehicle toward the target.
In certain cases it is undesirable to mount a tracker in the nose of the carrying vehicle. For example, in a torpedo it is desirable to have a shaped charge or the like in the nose, and if the nose must be utilized to carry a tracker, it is naturally not available for mounting the charge. As another example, it is sometimes desirable to reduce the aerodynamic drag on a missile by designing the nose to come to a sharp, sleek point. If a tracker is to be mounted in the nose, a certain amount of area is required to contain it, and it is difficult to design the missle to have a pointed nose without compromising optical performance. Further, the physical limits of the nose of a missile, torpedo or the like restrict the movements of physical components of a tracker mounted therein, and generally limit the viewing area of the tracker to a small cone directly in front of the carrying vehicle.
In addition to the above-mentioned problems, many prior art trackers, and especially those designed to enlarge the viewing cone, are designed in a manner whereby image rotation occurs at the sensing unit. Image rotation at the sensing unit is undesirable because it complicates the electronics system which must be used, and because it introduces human factors problems for any person viewing a display screen or the like showing the target.
The use of domes to contain various target tracking devices is well known. For example, the famed "Flying Fortress" of World War II had several domes which contained guns and large trackers, the trackers being human beings. However, the use of domes as large as those used on a B-17 or similar aircraft on a guided missile, torpedo or the like, and the sending of a human being along to guide the missile or torpedo to its target would be rather impractical to say the least. In fact, with small missiles, i.e., missiles having diameters of about 24 inches or less, the results obtained from using any external paraphernalia whatsoever (excepting necessary external paraphernalia such as fins) must be very carefully weighed against the adverse aerodynamic effects which might be produced. And, since certain equipment which must necessarily be used in automatic trackers has not been miniaturized to the point where it can be conveniently placed in a small dome which would have inconsequential drag effects on a missile or the like, dome mounted trackers have heretofore not been used on small diameter missiles or the like.